If you are into audio and kit building have a look at this cool JAN6418 Valve Preamplifier Kit Build. Not very many areas of electronics have kept tubes alive but this kit uses two of them as the heart of the circuit.
"Oatley Electronics in New South Wales Australia makes a few kits based around the Raytheon JAN6418 sub-miniature valve (tube). These 6418 valves look like small Christmas Tree lights. Hard to believe that they are actually pentodes. The USA made Raytheon JAN6418 sub-miniature valves are low power consumption pentodes that are used as triodes in the circuit. The 6418 tube filaments are 1.2V and draw just 10mA. You can barely see the tubes glowing in a dark room and the are just slightly warm to the touch. From a single 9V battery the entire preamplifier draws just 12mA. For a longer run time I used two 9V lithium batteries in parallel."
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Now I know what I’m going to do with all of those JAN tubes I have laying around. I must have at least a dozen or so. I’d have to check the numbers, though. From what I’ve been told by numerous sources, JAN= Joint Army/Navy. Basically, they’re unified part numbers by specification, not just part number.